Chemistry, The Central Science, 10th edition
Theodore L. Brown; H. Eugene LeMay, Jr.;
and Bruce E. Bursten
Chapter 11
Intermolecular Forces,
Liquids, and Solids
John D. Bookstaver
St. Charles Community College
St. Peters, MO
 2006, Prentice Hall, Inc.
Intermolecular
Forces
States of Matter
The fundamental difference between states of
matter is the __________ between particles.
Intermolecular
Forces
States of Matter
Because in the solid and liquid states
particles are closer together, we refer to them
as __________ phases.
Intermolecular
Forces
The States of Matter
• The state a substance is
in at a particular
temperature and
pressure depends on
two __________ entities:
 The __________ energy
of the particles
 The __________ of the
attractions between the
particles
Intermolecular
Forces
_____________ Forces
The attractions between molecules are not
nearly as strong as the __________
attractions that hold compounds together.
KNOW THE DIFFERENCE!
Intermolecular
Forces
Intermolecular Forces
They are, however, strong enough to control
__________ properties such as __________
and melting points, vapor pressures, and
viscosities.
Intermolecular
Forces
Intermolecular Forces
These __________ forces as a group are
referred to as van der Waals forces.
Intermolecular
Forces
van der Waals Forces
•
•
•
•
__________ -dipole interactions
__________ bonding
London __________ forces
Ion - Dipole forces
The next slides talk about each of these “in more
depth.”
Intermolecular
Forces
Ion-Dipole Interactions
• A fourth type of force, ion-dipole interactions
are an important force in solutions of ions.
• The strength of these forces are what make it
possible for __________ substances to
dissolve in __________ solvents.
Intermolecular
Forces
Dipole-Dipole Interactions
• Molecules that have
permanent dipoles are
attracted to each other.
 The positive end of one is
attracted to the negative
end of the other and viceversa.
 These forces are only
important when the
molecules are close to
each other.
Intermolecular
Forces
Dipole-Dipole Interactions
The more __________ the molecule, the
higher is its boiling point.
Intermolecular
Forces
London Dispersion Forces
While the electrons in the 1s orbital of helium
would repel each other (and, therefore, tend
to stay far away from each other), it does
happen that they __________ wind up on the
Intermolecular
same side of the atom.
Forces
London Dispersion Forces
At that __________, then, the helium atom is
polar, with an excess of electrons on the left
side and a shortage on the right side.
Intermolecular
Forces
London Dispersion Forces
Another helium nearby, then, would have a
dipole __________ in it, as the electrons on
the left side of helium atom 2 repel the
electrons in the cloud on helium atom 1.
Intermolecular
Forces
London Dispersion Forces
London dispersion forces, or dispersion
forces (this is what the Test calls them all the
time), are __________ between an
____________ dipole and an induced dipole.
Intermolecular
Forces
London Dispersion Forces
• These forces are present in all molecules,
whether they are __________ or nonpolar.
• The tendency of an electron cloud to
_________ in this way is called polarizability.
Intermolecular
Forces
Factors Affecting London Forces
• The __________ of the molecule
affects the strength of dispersion
forces: long, skinny molecules
(like n-pentane tend to have
stronger dispersion forces than
short, fat ones (like neopentane).
• This is due to the increased
__________ area in n-pentane.
Intermolecular
Forces
Factors Affecting London Forces
• The strength of dispersion forces tends to
increase with increased __________ weight.
• Larger atoms have larger electron clouds,
which are easier to __________.
Intermolecular
Forces
Which Have a Greater Effect:
Dipole-Dipole Interactions or Dispersion Forces?
• If two molecules are of comparable size
and shape, dipole-dipole interactions
will likely be the __________ force.
• If one molecule is much __________
than another, dispersion forces will likely
determine its physical properties.
Intermolecular
Forces
How Do We Explain This?
• The nonpolar series
(SnH4 to CH4) follow
the __________
trend.
• The polar series
follows the trend
from H2Te through
H2S, but water is
quite an
__________.
Intermolecular
Forces
Hydrogen Bonding
• The dipole-dipole interactions
experienced when H is bonded to
___, ___, or ___ are unusually
strong.
• We call these interactions
hydrogen bonds.
• MEMORIZE THESE 3
ELEMENTS!
Intermolecular
Forces
Hydrogen Bonding
Hydrogen bonding
arises in part from the
high _____________
of nitrogen, oxygen,
and fluorine.
Also, when hydrogen is bonded to one of those
very electronegative elements, the hydrogen
_______________ is exposed.
Intermolecular
Forces
Summarizing Intermolecular Forces
Intermolecular
Forces
Intermolecular Forces Affect
Many Physical Properties
The strength of the
__________
between particles
can greatly affect
the properties of a
substance or
solution.
Intermolecular
Forces
Viscosity
• Resistance of a liquid
to flow is called
viscosity.
• It is related to the ease
with which molecules
can move past each
other.
• Viscosity increases
with __________
intermolecular forces
and decreases with
higher temperature.
Intermolecular
Forces
Surface Tension
Surface
__________ results
from the net inward
force experienced
by the molecules on
the surface of a
liquid.
Intermolecular
Forces
Phase Changes
the stronger the IM forces,the more “energy” needed to
change phases.
Intermolecular
Forces
Energy Changes Associated
with Changes of State
• Heat of __________ : Energy required to
change a solid at its melting point to a liquid.
MEMORIZE THIS NAME!
Intermolecular
Forces
Energy Changes Associated
with Changes of State
• Heat of __________ : Energy required to
change a liquid at its boiling point to a gas.
MEMORIZE THIS NAME!
Intermolecular
Forces
Energy Changes Associated
with Changes of State
• The heat added to the
system at the melting and
boiling points goes into
__________ the
molecules farther apart
from each other.
• The __________ of the
substance does not rise
during the phase change.
Intermolecular
Forces
Vapor Pressure
• At any temperature, some molecules in a
liquid have enough energy to __________.
• As the temperature rises, the fraction of
molecules that have enough energy to
escape __________.
Intermolecular
Forces
Vapor Pressure
As more molecules
escape the liquid,
the __________
they exert
increases. The “gas
phase” molecules
(called a vapor)
have more collisions
with each other and
their container.
Intermolecular
Forces
Vapor Pressure
The liquid and vapor
reach a state of
__________
equilibrium: liquid
molecules
evaporate and vapor
molecules condense
at the same rate.
Intermolecular
Forces
Vapor Pressure
• The boiling point of a
liquid is the
temperature at which
its vapor pressure
equals __________
pressure.
• The __________
boiling point is the
temperature at which
its vapor pressure is
760 torr.
Intermolecular
Forces
Phase Diagrams
Phase diagrams display the state of a
substance at various __________ and
temperatures and the places where
__________ exist between phases.
Intermolecular
Forces
Phase Diagrams
• The AB line is the ________-vapor interface.
• It starts at the triple point (A), the point at
which all three states are in equilibrium.
Intermolecular
Forces
Phase Diagrams
It ends at the __________ point (B); above
this critical temperature and critical pressure
the liquid and vapor are indistinguishable
from each other.
Intermolecular
Forces
Phase Diagrams
Each point along this line is the __________
point of the substance at that pressure.
Intermolecular
Forces
Phase Diagrams
• The AD line is the interface between liquid
and solid.
• The __________ point at each pressure can
be found along this line.
Intermolecular
Forces
Phase Diagrams
• Below A the substance cannot exist in the
__________ state.
• Along the AC line the solid and gas phases
are in equilibrium; the sublimation point at
each pressure is along this line.
Intermolecular
Forces
Phase Diagram of Water
• Note the high
__________ temperature
and critical pressure:
 These are due to the
strong van der Waals
forces between water
molecules.
Intermolecular
Forces
Phase Diagram of Water
• The slope of the solid–
liquid line is __________.
 This means that as the
pressure is increased at a
temperature just below the
melting point, water goes
from a solid to a
__________. This seems
odd:-)
Intermolecular
Forces
Phase Diagram of Carbon Dioxide
Carbon dioxide
cannot exist in the
__________ state at
pressures below
5.11 atm; CO2
__________ at
normal pressures.
Intermolecular
Forces
Phase Diagram of Carbon Dioxide
The low critical
temperature and
critical pressure for
CO2 make
__________ l CO2 a
good solvent for
extracting nonpolar
substances (such as
caffeine).
Intermolecular
Forces
Solids
• We can think of
solids as falling into
two groups:
 __________—
particles are in highly
ordered
arrangement.
Intermolecular
Forces
Solids
 __________—no
particular order in the
arrangement of
particles.
Intermolecular
Forces
Attractions in Ionic Crystals
In ionic crystals, ions
pack themselves so as
to maximize the
attractions and
minimize repulsions
between the ions.
Intermolecular
Forces
Crystalline Solids
Because of the
order in a crystal,
we can focus on the
repeating pattern of
arrangement called
the unit cell.
Intermolecular
Forces
Crystalline Solids
There are several types of basic
arrangements in crystals, such as the ones
shown above.
Intermolecular
Forces
Crystalline Solids
We can determine
the empirical
formula of an ionic
solid by determining
how many ions of
each element fall
within the unit cell.
Intermolecular
Forces
Ionic Solids
What are the empirical formulas for these
compounds?
(a) Green: chlorine; Gray: cesium
(b) Yellow: sulfur; Gray: zinc
(c) Green: calcium; Gray: fluorine
(a)
(b)
CsCl
ZnS
(c)
CaF2
Intermolecular
Forces
Types of Bonding in
Crystalline Solids
Intermolecular
Forces
Covalent-Network and
Molecular Solids
• Diamonds are an example of a covalentnetwork solid in which atoms are covalently
bonded to each other.
 They tend to be hard and have high melting
points.
Intermolecular
Forces
Covalent-Network and
Molecular Solids
• Graphite is an example of a molecular solid in
which atoms are held together with van der
Waals forces.
 They tend to be softer and have lower melting
points.
Intermolecular
Forces
Metallic Solids
• Metals are not
covalently bonded, but
the attractions between
atoms are too strong to
be van der Waals
forces.
• In metals, valence
electrons are
delocalized throughout
the solid.
Intermolecular
Forces